Generally, portable electronic devices such as smart phones or tablet computers are widely used. As known, the physical key of the portable electronic device results in some drawbacks. For example, in case that the smart phone is equipped with the physical key, the physical key increases the size and weight of the smart phone. Moreover, the life span of the physical key is short, and the aesthetically-pleasing appearance is adversely affected. Nowadays, some portable electronic devices are equipped with virtual keys. However, the tactile feel provided by the virtual key is not comparable to the tactile feel of the physical key. Therefore, the benefits of the virtual key and the physical key should be taken into consideration.